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Jess8bit
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CarbonMike (23/06/2013)
fgayford (05/06/2013)
It almost looks like the epoxy is not cured to a hard state and the sanding dust is fusing into the soft surface?This without a doubt. I am a composite trimmer/fitter/laminator by trade, and have seen this happen many many times on virgin parts. Thank you CarbonMike  What I do now is I wait for 48hrs+ before demolding. What I could try is some post curing to reduc this delay, I guess.
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CarbonMike
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fgayford (05/06/2013)
It almost looks like the epoxy is not cured to a hard state and the sanding dust is fusing into the soft surface?This without a doubt. I am a composite trimmer/fitter/laminator by trade, and have seen this happen many many times on virgin parts.
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Jess8bit
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yep, should do that as well. It's a kind of (bad) habit I have, like if I was working with prepreg ^^
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wozza
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Unless the part is really complicated with lots of recesses and steep sides etc you should not really need to stick the first layer down. Just pull vac in stages ie pull a small amount of vac and close off the valve, position the bag carbon etc and pull some more vac. Continue this way until you have full vac and everything is in place and tight against the mould surface. If you are not happy just release some of the vac and start the process again.
Carbon Copies Ltd
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Jess8bit
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mmmm you're right, although I'm really carefull with applying a very light spray (knowing it might cause bonding issues since it is not a epoxy compatible spray), that could still explain the lack of bonding here or there, especially in the croner, where I spray a bit more to ensure cloth sticking. I guess I'll have to re-schedule my work so that I lay down the carbon while GC is still tacky (it was handy to let the night passes ^^). If only I could find a genuine tackifier... anyway, thank you Warren, for all
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wozza
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Ok 24 hours for the GC50 is ok but no longer  Ditch (stop using ) the spray tack. It is very easy to get a thick layer of it on edges and corners etc. When not using GC50 this is not really an issue as it will just effect the surface finish of the part which can be polished out but when using GC50 the spray tack forms a layer between the GC50 and the resin preventing a good bond between the two. Try the method I suggested before if you need to stick the carbon down
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Jess8bit
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I use 3M super spray 77. Not perfect I know... It's the only one I can find  (SprayZ still missing) I leave up to 24hrs (left it cure during the night) so it's not tacky anymore, following the guidelines from the EC (Matt) car bonnet video tut.
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wozza
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Jess8bit (16/06/2013)
Thank you Warren for your suppor In this case I assure you it is not a bridging problem, the picture may mislead you. I try another one :   The resin follows the carbon an d the mould perfectly (I use a spray gly to stick the cloth to the mold), and there is no bridging once demolded. It occured while sanding the border of the part, after having done a rough trimming with the Dremel. The Gel Coat peels off, under mechanical action, I'd say. Why so fragile ? Bad bonding between GC and the resin ? How much and what type of spray tack did you use? Also how long after the GC50 was laid down did you do the infusion?
Carbon Copies Ltd
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Jess8bit
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Group: Forum Members
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Thank you Warren for your suppor In this case I assure you it is not a bridging problem, the picture may mislead you. I try another one : The resin follows the carbon an d the mould perfectly (I use a spray gly to stick the cloth to the mold), and there is no bridging once demolded. It occured while sanding the border of the part, after having done a rough trimming with the Dremel. The Gel Coat peels off, under mechanical action, I'd say. Why so fragile ? Bad bonding between GC and the resin ?
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wozza
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Jess8bit (14/06/2013)
Ok so now I have a good surface finish, At least, no bubbles anymore (I let the resin flow some time after it reaches the outlet connector, then clamp off the vac line, then the feed line) But, as you can see on the picture below, I'm facing a new problem, that occured during the trimming step. More precisely, in the sanding step that comes after the Dremel trimming. It looks like the gel coat is delaminating. It's only 4 or 5 spots like this, and only on the part perimeter. As if it did not like me sanding with the permagrit files. What could these defects be the symptoms of ? |
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